There have been known fiber application machines, for applying on an application surface of a male or female mold, a wide band formed of at least a ribbon-type resin pre-impregnated flat fiber, particularly carbon fibers pre-impregnated with a thermoplastic or thermosetting resin, and particularly so-called fiber placement machines for applying a wide band formed of a plurality of resin pre-impregnated fibers.
These fiber placement machines, such as described in patent document WO2006/092514 typically comprise a fiber placement head and a system for moving said fiber application head. Typically, said fiber placement head comprises a compacting roller for contacting the mold so as to apply the pre-impregnated fiber band, a guiding assembly for guiding fibers in the form of a band over said compacting roller, and a heating system for heating the pre-impregnated fibers.
The compacting roller presses the fiber band against the mold application surface, or against the fiber band or bands deposited beforehand, such that the adhesion of the deposited bands between each other is facilitated, and air trapped between the deposited bands is progressively discharged.
The heating system heats the pre-impregnated fiber band, and/or the mold or the bands already applied upstream of the compacting roller, just before the compacting of the band, so as to at least soften the resin and thus promote the adhesion of the bands between each other. Generally, the band heating system provides at least the heating of the band just before its compacting.
In order to ensure a substantially uniform compacting over the entire width of the band, the fiber placement head advantageously comprises a compacting roller able to adapt to the application surface, and preferably, a compacting roller made of a flexible material, which is elastically deformable, generally, an elastomeric material.
In the case of thermosetting resins, the pre-impregnated fibers are only heated to be softened, typically at temperatures of about 40° C. At these temperatures, an elastomeric material flexible roller may advantageously be used. After applying several layers of superimposed bands, the resulting part is vacuum hardened, through polymerization, by passing it within a furnace, generally an autoclave furnace.
In the case of thermoplastic resins, the pre-impregnated fibers have to be heated at higher temperatures, at least up to the resin melting temperature, that is, of about 200° C. for nylon type resins, and of about 400° C. for PEEK type resins. A hardening operation, called consolidation operation, of the resulting part is advantageously carried out thereafter by passing it within a furnace.
The heating carried out during the application of the band may be implemented through a laser type heating system so as to obtain a concentrated and sharp heating. Owing to the high heating temperatures, the fiber placement heads are provided with heat resistant metallic compacting rollers which may also be cooled from inside via a waterway.
To adapt to the profile of the application surface, there have been proposed segmented metallic compacting rollers, comprising several independent roller segments mounted abreast on a same axis, each segment being independently and radially movable, and being elastically biased against the application surface. Nevertheless, the structure of such segmented metallic rollers and their implementation proved to be complex.
Flexible rollers formed from a so called high temperature elastomeric material, including a heat stabilizer, have also been tested. Nevertheless, theses rollers proved to be unsatisfactory for the implementation of thermoplastic resins.
To make it possible to use a flexible roller at the operating temperatures of the thermoplastic resins, there has been proposed, notably in patent document FR 2 878 779, a head provided with two compacting rollers with a heating system acting between both rollers and outputting a heat radiation substantially perpendicular to the band, between both rollers. Such a dual roller head exhibits a greater encumbrance inhibiting fiber deposition on certain application surface profiles. Moreover, the heating of the bands deposited beforehand for their adhesion through welding to the newly applied band is only made through thermal conduction, which constitutes a restrictive factor for the fiber application speed.